1. Field of the Invention
The present invention relates to an interface device, to which an analog picture signal is inputted and converted to a digital display signal, and to a converting circuit for converting a digital display signal to an optimum digital display signal, and more particularly, to a display device having an interface device capable of preventing the degradation of the resolving power of a gray scale corresponding to an analog picture signal, and of reproducing proper luminance, which corresponds to an analog picture signal, and to a display device having a converting circuit for preventing the degradation of the resolving power of a gray scale corresponding to a supplied display signal.
2. Description of the Related Art
A flat display device, such as a plasma display device for a large screen, which can provide a high-lightened display, a middle or small type liquid crystal display, has been provided that satisfies a demand for thinning and reducing the size of display device for a computer or a home TV video receiver. These flat display devices include an interface device, to which an analog picture signal is ordinarily input, converting the input signal into a digital display signal and driving a display panel according to the digital display signal.
The digital display signal of these flat display devices is generated by quantizing (analog-digital converting) the analog picture signal in an analog-digital converter of the interface device. A maximum standard value of the analog picture signal is fixed to a dynamic range of the analog-digital converter in the conventional interface device.
FIG. 15 shows a relationship between the analog picture signal and the converted digital display signal in the conventional plasma display device. An analog picture signal Vin having a ramp waveform and digital display signals D0 to D7, which are analog-digital converted in the interface device, are shown in FIG. 15. A luminance control signal BCA, which is adjusted from an external device, and a luminous frequency Fsus corresponding to the luminance control signal BCA are also shown in FIG. 15. In FIG. 15, both the luminance control signal BCA and the luminous frequency Fsus are respectively fixed to each maximum value.
In the example of FIG. 15, a maximum amplitude level of the analog picture signal Vin is equivalent to a dynamic range Vref of the analog-digital converter (approximately 100%) in a frame K, while the level is approximately 50% of the dynamic range Vref in a frame K+1. Further, the level is approximately 25% of the dynamic range Vref in a frame K+2.
In this case, in the frame K, the analog picture signal Vin is allocated all for the number of gray scales represented by the 8-bit digital display signals D0 to D7. In other words, the maximum number of luminous gray scales (256 gray scales) is employed in the frame K, while the analog picture signal Vin is allocated only for the number of gray scales (128 gray scales) represented by 7-bit digital display signals in the frame K+1. Further, in the frame K+2, the analog picture signal Vin is allocated only for the number of gray scales (64 gray scales) represented by 6-bit digital display signals.
As described above, since the maximum standard value uniformly corresponds to the dynamic range Vref for the analog picture signal in the conventional interface device, the luminance of converted digital display signal can be displayed, as it is. However, this causes a problem such that the resolving power of gray scales is reduced, when the analog picture signal Vin represents a comparatively dark picture having only a lower luminous region, like the frame K+2. If an insufficient resolving power of gray scales is given to such the dark picture, it is impossible to represent the luminance (brightness) smoothly changing in the dark picture, thereby lacking a detail expression for the picture.
Further, there are also cases, wherein the display device is directly supplied with a digital display signal from a computer or other external machine, and displays an image in accordance therewith. In this case, the same as described above, when a picture is relatively dark, the supplied display signal may not be making use of all of the full range of the gray scales thereof, and when this happens, it is only possible to provide insufficient gray scale resolving power (gray scale resolution) for a dark picture.
Accordingly, it is an object of the present invention to provide a display device including an interface device whereby a digital display signal having a resolving power of gray scales enough to represent a dark picture can be generated.
To achieve the above-described objects, an interface device according to the present invention is provided to prevent from reducing a resolving power of luminous gray scales by setting a dynamic range of an analog-digital converter according to a peak value of an analog picture signal. Further, a luminance control signal for determining a luminous level of the picture to be displayed is set according to the peak value of the analog picture signal. In the interface device according to the present invention, therefore, even when a dark picture, of which analog picture signal level is comparatively small, is displayed, a display signal for displaying a picture having a sufficient resolving power of gray scales with a luminance (brightness) required for the darkness of the picture can be generated.
FIG. 1 is a structural diagram of a plasma display device according to the present invention.
FIG. 2 shows a relationship between an analog picture signal and converted digital display signals in the plasma display device according to the present invention.
FIG. 3 is a diagram showing a relationship between a luminance frequency Fsus and number of sustain discharges in each sub-frame.
FIG. 4 is a diagram showing a relationship of the analog picture signal, a dynamic range and the maximum luminance value.
FIG. 5 is a table showing a relationship between the dynamic range and the luminance control signal for six type picture signals.
FIG. 6 shows a structure of the dynamic range and a luminance control signal generating section according to the present invention.
FIG. 7 is a detailed circuitry diagram of a signal level detecting circuit according to the present invention.
FIG. 8 is a circuitry diagram of a dynamic gray scale controller 12 and a dynamic luminance controller 13 according to the present invention.
FIG. 9 is a block diagram of a plasma display device in a second embodiment.
FIG. 10 is a diagram of a histogram showing the distribution state of digital display signals in a gray scale controlling circuit 20.
FIG. 11 is a diagram showing the constitutions of a gray scale controlling circuit and a display signal converting circuit.
FIG. 12 is a table showing the relationship between histogram distributions and selection signals, and a diagram showing examples of the conversion tables therefor.
FIG. 13 is a diagram for explaining the operation of a luminous frequency controller.
FIG. 14 is a table showing the relationship between different histogram distributions and selection signals, and a diagram showing examples of the conversion tables therefor.
FIG. 15 is a diagram showing a relationship between the analog picture signal and the converted digital display signal in the conventional plasma display device.